Author: whitequark Date: Mon Dec 25 09:05:07 2017 New Revision: 321445 URL: http://llvm.org/viewvc/llvm-project?rev=321445&view=rev Log: [libunwind] Add proper support for DWARF unwind on bare metal.
Right now, ARM EHABI unwind on bare metal expects to find the symbols __exidx_start and __exidx_end defined, and uses those to locate the EH tables. However, DWARF unwind on bare metal expects to find dl_iterate_phdr, which, although possible to provide, is inconvenient and mildly absurd. This commit provides feature parity with ARM EHABI unwind by looking for symbols __eh_frame_start, __eh_frame_end, __eh_frame_hdr_start and __eh_frame_hdr_end, denoting the start and end of the sections with corresponding names. As far as I know, there is no de jure or de facto ABI providing any such names, so I chose the obvious ones. The .eh_frame_hdr support is optional for maximum flexibility and possible space savings (e.g. if libunwind is only used to provide backtraces when a device crashes, providing the .eh_frame_hdr, which is an index for rapid access to EH tables, would be a waste.) The support for .eh_frame_hdr/DWARF index in the first place is conditional on defined(_LIBUNWIND_SUPPORT_DWARF_INDEX), although right now config.h will always define this macro. The support for DWARF unwind on bare metal has been validated within the ARTIQ environment[1]. [1]: https://m-labs.hk/artiq/ Modified: libunwind/trunk/src/AddressSpace.hpp Modified: libunwind/trunk/src/AddressSpace.hpp URL: http://llvm.org/viewvc/llvm-project/libunwind/trunk/src/AddressSpace.hpp?rev=321445&r1=321444&r2=321445&view=diff ============================================================================== --- libunwind/trunk/src/AddressSpace.hpp (original) +++ libunwind/trunk/src/AddressSpace.hpp Mon Dec 25 09:05:07 2017 @@ -83,6 +83,38 @@ namespace libunwind { } #endif +#elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_IS_BAREMETAL) + +// When statically linked on bare-metal, the symbols for the EH table are looked +// up without going through the dynamic loader. + +// The following linker script may be used to produce the necessary sections and symbols. +// Unless the --eh-frame-hdr linker option is provided, the section is not generated +// and does not take space in the output file. +// +// .eh_frame : +// { +// __eh_frame_start = .; +// KEEP(*(.eh_frame)) +// __eh_frame_end = .; +// } +// +// .eh_frame_hdr : +// { +// KEEP(*(.eh_frame_hdr)) +// } +// +// __eh_frame_hdr_start = SIZEOF(.eh_frame_hdr) > 0 ? ADDR(.eh_frame_hdr) : 0; +// __eh_frame_hdr_end = SIZEOF(.eh_frame_hdr) > 0 ? . : 0; + +extern char __eh_frame_start; +extern char __eh_frame_end; + +#if defined(_LIBUNWIND_SUPPORT_DWARF_INDEX) +extern char __eh_frame_hdr_start; +extern char __eh_frame_hdr_end; +#endif + #elif defined(_LIBUNWIND_ARM_EHABI) && defined(_LIBUNWIND_IS_BAREMETAL) // When statically linked on bare-metal, the symbols for the EH table are looked @@ -348,6 +380,20 @@ inline bool LocalAddressSpace::findUnwin info.compact_unwind_section_length = dyldInfo.compact_unwind_section_length; return true; } +#elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_IS_BAREMETAL) + // Bare metal is statically linked, so no need to ask the dynamic loader + info.dwarf_section_length = (uintptr_t)(&__eh_frame_end - &__eh_frame_start); + info.dwarf_section = (uintptr_t)(&__eh_frame_start); + _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: section %X length %x", + info.dwarf_section, info.dwarf_section_length); +#if defined(_LIBUNWIND_SUPPORT_DWARF_INDEX) + info.dwarf_index_section = (uintptr_t)(&__eh_frame_hdr_start); + info.dwarf_index_section_length = (uintptr_t)(&__eh_frame_hdr_end - &__eh_frame_hdr_start); + _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: index section %X length %x", + info.dwarf_index_section, info.dwarf_index_section_length); +#endif + if (info.dwarf_section_length) + return true; #elif defined(_LIBUNWIND_ARM_EHABI) && defined(_LIBUNWIND_IS_BAREMETAL) // Bare metal is statically linked, so no need to ask the dynamic loader info.arm_section = (uintptr_t)(&__exidx_start); _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
